1. Field
Aspects of embodiments of the present invention relate to an organic light emitting display device.
2. Description of the Related Art
With the development of an information-driven society, the demand for various types of display devices for displaying an image is increasing. Various flat panel displays such as liquid crystal displays (LCDs), plasma display panels (PDPs), and organic light emitting diode (OLED) displays have been widely used in recent years. Among the flat panel displays, OLED displays are driven at a relatively low voltage, are relatively thin, have a relatively wide viewing angle, and have a relatively quick response speed.
A display panel of the OLED display may include a plurality of pixels arranged in a matrix form. Each of the pixels may include a scan transistor for supplying a data voltage of a data line in response to a scan signal of a scan line and a driving transistor for adjusting the amount of the current supplied to an organic light emitting diode in accordance with a voltage supplied to a gate electrode. The drain-to-source current Ids of the driving transistor supplied to the organic light emitting diode can be expressed according to the following equation:Ids=k·(Vgs−Vth)2  (1)where k represents a proportionality coefficient determined by the structure and physical properties of the driving transistor, Vgs represents the gate-source voltage of the driving transistor, and Vth represents the threshold voltage of the driving transistor.
The drain-to-source current Ids of the driving transistor depends upon the threshold voltage Vth of the driving transistor. However, the threshold voltage Vth of the driving transistor may differ (or vary) due to process error (e.g., variability in the manufacturing processes). Alternatively, the threshold voltage Vth of the driving transistor may shift or change as the driving transistor degrades (or ages) over time. Therefore, the threshold voltage Vth of the driving transistor may differ from pixel to pixel. As a result, the luminance of light emitted from each of the pixels may differ even if the same data voltage is supplied to the pixels.